The process for manufacturing flexible graphite is well known. In the typical practice and as described in U.S. Pat. No. 3,404,061, the disclosure of which is incorporated herein by reference, flakes of natural graphite are intercalated in an acid solution. After the flakes are intercalated they are washed and dried and then exfoliated by exposure to high temperature or under a flame for a short period of time. This causes the flakes to expand or exfoliate in a direction perpendicular to the crystalline planes of the graphite. The exfoliated graphite flakes are vermiform in appearance and are therefore commonly referred to as worms. The worms may be compressed into sheets or foils with a density approaching theoretical density, although a density of about 70 lbs/ft.sup.3 is considered typical for most applications. The sheets of flexible graphite can be cut into any desired configuration to suit a particular application.
It is common to cut thin flexible graphite sheets of between 2-70 mils in thickness into narrow strips of less than about 1/4" wide which may then be interwoven into a braided product, spirally wound into a spiral wound gasket or die cut into various sizes for use as a gasket or packing material.
Unfortunately flexible graphite is relatively weak in tensile strength and the narrow strips may tend to break when subjected to bending during handling particularly in the fabrication of a braided or spiral wound product. The weakness in tensile strength may be overcome by attaching very fine long threads of cotton or polymide to the flexible graphite to serve as reinforcement. The threads are adhesively bonded to the sheets of flexible graphite before they are cut into strips. Not only is this method expensive but the use of an adhesive has the potential of gumming up the machinery for cutting the flexible graphite into strips. Another method of reinforcing flexible graphite is to interpose a layer of a material strong in tensile strength between two flexible graphite sheets. The interlayer may be attached to the sheets of flexible graphite using any commercial contact adhesive. Again this method involves using an adhesive which is not only costly but substantially increases the percentage of non-flexible graphite in the final product and unnecessarily adds to the thickness of the final product. Moreover the adhesive may vaporize upon heating leaving a porous body which permits leakage. In addition a thermoplastic adhesive will soften at elevated temperature and increase the probability of shear failure. At present, however, there is no known method for reinforcing flexible graphite without using an adhesive.